Environmentally Safe Silane Technology for Adhesion of Rubber to Tire Cord Steel

Strong and durable bonds between rubber and metals are important in many industries. The largest single commercial application is bonding of steel tire cords to sulfur-vulcanized natural rubber (NR) compounds. The current process for bonding steel tire cords to NR compounds requires the plating of brass on the individual filaments. This brass alloy is applied on the running wire as it is being drawn by electrodeposition from a cyanide plating bath. Alternatively, thin films of copper and zinc are plated sequentially, and the wire is heated so as to diffuse the copper and zinc layers. The use of the brass plating bath, especially when cyanide baths are used, causes serious environmental and waste disposal problems. However, no rubber-steel bonding process that provides the same performance as the brass coating process in terms of aged adhesion and dynamic adhesion has ever been put forward. In nontire automotive rubber-bonding applications, the brass plating process is not used, but is replaced with a two-step solvent-based adhesive process. These adhesives contain low molecular weight rubbers, silanes, fillers, crosslinkers, antioxidants, thickeners, and other components. The two steps comprise a primer coat and a topcoat, and contain relatively large amounts of flammable organic solvents such as toluene, xylene, and others. Water-based adhesives have been proposed but are not yet widely used because their performance lags behind as compared with the solvent-based materials. Although they demonstrate excellent performance for bonding different types of rubber to various metals, the solvent-based adhesives suffer from serious environmental shortcomings because they require the collection and disposal of solvents.